1. Field of the Invention
The present invention relates to an envelope generator for electronic musical instruments which generates a wide variety of envelopes by controlling speed parameters representative of the speeds of attack, decay and release of an envelope and which has a reduced number of input terminals.
The present invention also pertains to an envelope generator for electronic musical instruments which is designed to form envelope waveshapes for various amplitude modulation effects and control their volume levels with a simple arrangement.
Further, the present invention also concerns an envelope control device for electronic musical instruments, and more particularly a system for controlling an envelope generator for generating an envelope waveshape through utilization of digital parameters.
2. Description of the Prior Art
Conventional systems for digitally generating an envelope are roughly divided into those of storing a waveshape and those of approximating a waveshape by functions.
In the case of generating many kinds of envelopes of different waveshapes such as an envelope for a sliding Formant filter for changing a harmonic coefficient of a musical note as described, for example, in U.S. Pat. No. 4,085,644, an envelope for amplitude modulation and so forth, the former systems call for a number of memories, and hence are uneconomical and the latter systems are mostly of the type controlling the oscillation frequency of a CR oscillator to provide timing for functional operations, so that they must be provided with oscillators corresponding to tones of many kinds of envelopes and the number of input terminals used also increases. Accordingly, it is inevitable at the present stage of this field that the conventional systems are appreciably restricted by limitations on their arrangements and costs. With a view to simplifying the system arrangement, there has been proposed a system that accumulates a selected one of digital numbers of one group by an accumulator to obtain envelope calculating timing from its multi-bit output, but this system still involves an appreciably complicated arrangement associated with the accumulator.
In the past, amplitude modulation effects have widely been adopted in electronic musical instruments; they are a repeat effect for repeatedly generating an attennated sound as in a marimba, banjo, mandolin or the like, a crescendo effect for causing a gradual increase in loudness in an ensemble of string instruments, an attack effect for placing special emphasis upon the rise-up portion of a sound and so forth. These effects are usually produced by the use of an analog multiplier but the analog multiplier has the defects of small dynamic range, poor signal-to-noise ratio, low response speed and the necessity of adjustment of correcting dispersion in the characteristics of individual elements. Such effects can also be produced by a digital multiplier but a complex circuit arrangment is needed; especially, each amplitude modulated signal must be produced by an independent circuit, presenting a problem of high manufacturing costs.
In the prior art, the envelope waveshape is determined dependent on the time constant of a CR circuit in an analog envelope generator or the magnitude of the oscillation frequency of a CR oscillator in a digital envelope generator. In the case of requiring many kinds of envelopes, however, it is necessary to prepare CR circuits or CR oscillators corresponding in number to the kinds of envelopes needed.
U.S. Pat. No. 3,952,623 has proposed a solution to such a problem. In this U.S. patent it is proposed to accumulate a scale factor by an accumulator and to utilize the resulting signal as envelope calculation timing, but this method requires an accumulator for timing generation.
Further, an analog variable resistor is employed in conventional electronic musical instrument for controlling an envelope waveshape or tone but, in a digital electronic musical instrument, the resistance value of this analog variable resistor is converted to digital form for use as a digital quantity. However, the data merely converted to digital form cannot be used as it is; since different data are provided according to changing characteristics of the analog variable resistors, it is necessary to convert the data to desired characteristics. For example, in Japanese Patent Laid Open Gazette No. 149614/79 (laid open Nov. 24, 1974) in the name of the assignee of this application, there is proposed, for synthesizing a harmonic coefficient corresponding a musical note, data obtained by A-D conversion of the voltage value of a variable resistor is further converted into desired data. But the method of unitarily converting the value of the variable resistor cannot be applied as it is to the envelope control. That is to say, the change characteristic of an attack VR (VR being a variable resistor) for controlling the rise time of an envelope and the change characteristic of a decay VR for controlling the fall time of the envelope differ with respect to the envelope time and, further, in the case of causing a change in the tone of the sound to be produced (a sliding Formant filter effect), another VR is required.